Concerns have been raised recently about post-trial access to studied interventions in clinical trials, especially for vulnerable populations like the uninsured. These and other issues affecting the participation of vulnerable populations in human subjects research raise issues of the fair distribution of the risks, burdens and benefits of research. Yet little empirical data exists about factors that predict post-trial access, nor about the composition, motivation and experience of research volunteers. Our proposed study seeks to: 1) Describe post-trial access to care among participants in clinical trials, including access to the studied intervention or a therapeutic equivalent, and to assess whether insurance status is an independent predictor; and 2) Test associations between insurance status and selected aspects of the clinical trial experience, including reasons for enrollment/disenrollment, handling of adverse events, and participation in multiple trials as a means of obtaining access to care. To accomplish these aims, we will survey a national sample of volunteers in late phase clinical trials of type phase IIIB and IV at 3 points in time: upon enrollment; upon exit from the trial, and approximately 6 months after the trial ends. The proposed research is intended to gather empirical data on the experience of human subjects in clinical research that may reflect ethical aspects of the research enterprise (but not to assess ethical conduct of any particular trial), and to provide empirical information that will help to evaluate the just distribution of the risks and burdens of research.